A Monopoly can only be good if,it,has honesty,integrity as well as the trust of those it serves. It's unlikely in a society where greed is seen as good by those who run things.
Competition is good to the extent it serves the customer by cutting prices.
However too much competition will likely cause goods and services to be cut in quality in order to sell them at a deep discount. Further more price cutting by companies that have an economic advantage tends to allow them to undercut their competitor's on price. Even going as far as lowering their own retail price's in order to put their competitor's out of business.Or forcing them to sell out to them as the only alternative.
This is why the people need to control the wealthy. In order to protect themselves from greed and immoral behavior on behalf of the rich who would rule over the rest of humanity by using their vast wealth as a club over their heads.
The Greeks had the right idea concerning putting people in government by casting lots as picking a name out over hundreds as an example at random. Then voting for the few from the many sounds good to me! At,least we the people - not special interests would be able to not only elect but select who runs.